Ultrasonic fuel and air mixer



9, 1962 v. o. OLMSTEAD 3,016,233-

ULTRASONIC FUEL AND AIR MIXER Filed Nov. 6, 1959 l 'l 2/ Fue 0| Fig./ I

| 1| ran"; l/2 Box I d A J L. Trans near {g} p w::- .1 f I L. I Oil Transducer INVENTOR. Von D. Olmsfead bwospww ATTORIgEY United States. Patent 3,016,233 ULTRASONIC FUEL AND AIR MIXER Van D. Olmstead, Liverpool, N. Filed Nov. 6, 1959, Ser. No. 851,380 '5 Claims. (Cl. 26181) 7 This inventipn relates to a liquid fuel burner construction, and more particularly to a new and improved arrangement for producing atomization of the liquid fuel, prior to combustion thereof.

The efficiency and thoroughness of combustion of liquid fuels depend upon the ability of the liquid fuel burner to atomize the fuel involved. That is to say, the more highly atomized the fuel is, the more efficient is the combustion. This necessarily follows from the fact that the best way to provide a complete combustion reaction is to provide the highest possible reactive agent concentrations. If particles of virtually molecular dimensions could be supplied to the burner, then liquid fuel could be burned as efiiciently as gaseous fuel. This is the aim of the conventional gun-type or jet-type liquid fuel burner, but such a burner obviously falls far short of perfect atomization. In addition, such a burner requires a higher volume of air (for atomization) than is necessary for complete combustion; this results in much higher stack losses than are necessary. Also, the design (nozzles, jets, etc.) of previous liquid fuel burners requires that each be used only with the very small range of liquid fuels for which it is particularly designed.

An object of this invention is to provide an atomization arrangement for liquid fuel burnerswhich will give greatly improved atomization of the fuel, as compared with prior devices, and thus also greatly improved efficiency.

Another object is to provide an atomization arrangement for liquid fuel burners which will permit the buming of an almost unlimited range of liquid fuels, without any modification of the burner.

A further object is to provide a novel liquid fuel burner construction, including an atomization arrangement, which can be rather cheaply'constructed. At the same time, the liquid fuel burner as a whole provides greater safety and freedom from explosion than do gaseous fuel burners now in existence.

The objects of this invention are accomplished, briefly, in the following manner:

A liquid fuel, such as oil, is gravity-fed onto a plurality of ultrasonic wave vibrators arranged in labyrinthine form in an atomization chamber. These vibrators are arranged perpendicularly to the direction of the fuel flow through the chamber. The droplets of fuel, cascading down over the driven vibrators, are atomized, and the atomized fuel is removed from the chamber by a low volume stream of air, this stream forcing the atomized fuel through a funnel-type gun. At the end of this gun the atomized mixture is ignited, and combustion takes place. Fuel remaining unatomized after cascading over the vibrators or ribbons is collected in a sump at the bottom of the atomization chamber, from whence it is pumped back to the fuel reservoir or tank.

A detailed description of the invention follows, taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a side elevation illustrating somewhat schematically the overall arrangement of a liquid fuel burner of the invention;

FIGURE 2 is a section through the atomization chamber portion of the burner, taken on line L-Z of FIG- URE 1; and

FIGURE 3 is a section through a portion of the interior of the atomization chamber, taken on line 33 of FIGURE 2.

Referring first to FIGURE 1, liquid fuel '(e.g., socalled furnace oil) flows downwardly through a pipe 1 Patented Jan. 9, 1962 from an elevated reservoir or storage (supply) tank 2 toward the upper end of a prismoidal or box-like hollow atomization chamber 3. Itwill be noted that ordinary gravity feed is used, going into the chamber 3. As shown in FIGURE 2, the feed pipe 1 extends into the interior of chamber 3, at the upper end thereof, by way of a suitable aperture provided in the top wall of such chamber. At its lower end, pipe 1 is provided with a shower head arrangement 4 (see FIGURE 2), which functions to break up or separate the oil flowing down through pipe 1 into a plurality of fine streams which are distributed over a rather large area. Alternatively, a group of horizontally-positioned and radially-extending perforated pipes could be used here, the inner ends of these pipes being attached to the lower end of pipe 1 and communicating therewith. In other words, what is needed here is a means of distributing or spreading out the fuel oil over a rather extensive horizontal area which approximates the area of the top wall of chamber 3.

Whatever means is provided for spreading out the fuel oil at the top of chamber 3, so that the individual streams are distributed over a rather large horizontal area, the direction of fuel flow in chamber 3 is generally downward, from the top wall of this chamber toward the bottom thereof. A plurality of ribbons or reeds 5 are positioned in atomization chamber 3 below head 4, each of these ribbons extending substantiallyhorizontally across the chamber and thus in a direction perpendicular to the flow of fuel through the chamber. These ribbons,

which can be stamped out of sheet metal for example (though they might be made of plastic in some cases), are designed to be driven or vibrated at a predetermined frequency in the ultrasonic frequency range (such as 100 kc. for for example), and thus may be thought of as ultrasonic compressional wave vibrators. As .illustrated in FIGURE 3, these ribbon-like vibrators 5 are arranged in horizontal rows, there being a plurality of spaced vibrators in each row and adjacent rows being staggered or offset, so that the vibrators may be said to be arranged in maze or labyrinthine form, proceeding from the top of the chamber to the bottom thereof. This labyrinthine arrangement causes the liquid fuel, as it flows downward-- form offers the greatest possibility of action on each fuel droplet.

The vibrators or ribbons 5 are arranged to be driven at a frequency in the ultrasonic range from an electrically-powered transducer unit 6, which unit converts electrical energy to ultrasonic (compressional wave) energy. For this purpose, one end of each of the compressional wave vibrators 5 is attached to a plate 7 which is positioned near one side wall of chamber 3 and is driven or vibrated at ultrasonic frequency by means of a driving or actuating member 8 one end of which is secured thereto. Driving member 8 extends through one side wall of chamber 3, about at the center of this wall, and is in turn mechanically driven by the output of transducer (or oscillator) 6, operating at the ultrasonic frequency and positioned outside the chamber 3. The opposite end of each of the vibrators 5 is supported from that side wall of chamber 3 opposite to the side wall thereof through which member 8 extends, the support or mounting here being by means of suitable flexible couplings (indicated at 9 in FIGURE 2) which support the individual vibrators while permitting vibration thereof at the ultrasonic frequency rate.

As described, the vibrators 5 are mechanically driven so that they vibrate at a predetermined ultrasonic frequency. As the liquid fuel droplets issuing from head 4 cascade down over the ribbons 5 (which ribbons, as described, are vibrating at ultrasonic frequency rates), the fuel is atomized due to the action on the droplets of the ultrasonic wave energy. The action occurring here is similar to that which occurs when aerosols are formed by the use of ultrasonic waves; aerosols correspond to atomized liquids, or to dispersions.

The design of the ultrasonic generator or transducer 6 would depend on several things. First, there should be taken into consideration the natural frequencies to which the liquid fuel (oil) would respond, as well as the frequencies at which the vibrating ribbons would vibrate best. Then, too, the power required from the generator should be considered. For a heat rate (from the furnace) of 300,000 B.t.u. per hour, approximately 2 gallons of oil/ per hour must be atomized, which means about 126 cc.

per minute, or a little more than 2 cc. per second. Something less than 100 watts output (from generator 6) would be suitable for this. A unit 6 of this power, in which a very narrow frequency band of output is desired in the ultrasonic range, could be built rather inexpenproviding such a low volume flow of air will ordinarily be rather quiet in operation.

Any suitable means (e.g., a metallic screen positioned transversely or crosswise in gun portion 12) can be utilized to prevent flashbacks from the combustion chamber or fire box 13 to atomization chamber 3. In addition, since generator 6 is an electronic device, safety features can be easily incorporated therein, in accordance with known electronics practice. Thus, the liquid fuel burner of the present invention providesgreater safety and freedom from explosion than existing burners for gaseous fuel. I

It is pointed out that, with the burner of the present invention, the size of the oil molecule is not important,

sively using modern manufacturing techniques, such as printed circuitry, etc. Vacuum tubes are inexpensive and very reliable, while transformer costs would be very little more than those of the ignition transformers used in present oil burners. Such an arrangement would be extremely quiet; there would be no audible noise at all from the generator 6 and vibrators 5.

A centrifugal blower 10 is positioned adjacent one of the two remaining side walls (i.e., the side walls other than the one through which driving member 8 extends and the one associated with couplings 9) of the atomization chamber 3, and the discharge end of this blower is coupled through an aperture provided in this same side wall to the interior of chamber 3. Blower 10 operates to create a flow of air across chamber 3, in a direction from left to right in FIGURE 1. Blower 10 operates to provide only a very low volume flow of air across chamber 3, such as to move the atomized oil out of chamber 3 in a manner described hereinafter.

The fourth side wall of chamber 3 comprises the discharge end of the burner, by way of which the atomized fuel moves from the atomization chamber into the system combustion chamber. This last-mentioned chamber side wall is delineated by the larger end of a funnel member 11 which extends outwardly from chamber 3. The funnel member 11 and a tubular member 12 together comprise a funnel-type gun. One end of member 12 is coupled to the smaller end of funnel member- 11 and the other end of member 12 is placed in the fireg box 13 of a more or less conventional furnace. t

In operation, the oil flowing from reservoir 2 into atomization chamber 3 by way of pipe 1 is atomized by the action of compressional wave (ultrasonic) vibrators 5, as previously described. The atomized oil is moved by the blower 10 through the funnel-type gun from the chamber 3 to the fire box or system combustion chamber 13, where an electric ignition arrangement (not shown) ignites the mixture. The combustion process then takes place.

The magnitude of the low volume flow of air provided by blower 10 is governed mainly by the size of the vapor particles it is desired to move out of chamber 3. The blower must supply only enough air to move the proper or desired size vapor particles through the gun" nozzle 12. Too high a velocity would result in condensation on the gun walls, thus returning more oil to the sump to be described. In connection with the flow of air from blower 10, it is pointed out that, if atomization in the chamber 3 is complete enough, stack draft air (controlled by furnace damper 14) might be suflicient to supply combustion needs, thus rendering it unnecessary for blower 10 to supply any air for combustion. A blower to that of existing gaseous fuel burners.

nor is its viscosity, since substantially perfect atomization is eifected in all cases. Thus, relative to prior oil burners (whose nozzles can handle only fuels for which they are specifically designed), the burner of the present invention can handle a much wider range of liquid fuels, and in fact, almost an unlimited range of liquid fuels can be handled.

Since transducer or generator unit 6 and vibrators 5 create no audible noise, and since blower 10 is so quiet in operation, the liquid fuel burner of the present invention has a silence in operation comparable to that of existing gaseous fuel burners.

The liquid fuel burner of the present invention has fewer moving parts thando prior oil burners. Thus, maintenance problems are greatly simplified.

The device of the invention (including the ribbons 5), with the possible exception of the gun, can be manufactured completely from sheet metal stampings. Thus, it would entail a lower manufacturing cost than existing liquid fuel burner devices, a cost, in fact, comparable to that of existing gaseous fuel burners. Contributing to this cost reduction is the fact that the blower 10 can be considerably smaller than that required by the conventional oil burner.

It is stressed that the device of the present invention provides substantially complete atomization of the fuel. The labyrinthine form of the vibrators 5, oflering as it does the greatest possibility of action on each fuel droplet as the fuel cascades downwardly over the vibrators, contributes importantly to this substantial degree of atomization. In fact, with this invention, particles of virtually molecular dimensions are supplied from the atomization chamber 3 to the burner. This means that the efiiciency of the burner of the invention is comparable Contributing to the high efliciency obtainable with the present invention is the fact that only the air necessary for combustion is supplied to the burner in fire box 13; no excess air is supplied to this burner and stack losses are therefore no higher than absolutely necessary.

One possible problem might arise should unatomized oil collect at the bottom of the atomization chamber 3, after dripping off the lowest layer of ribbons 5. Such oil is prevented from accumulating in chamber 3 by the means now to be described. The bottom wall of chamber 3 is delineated by the larger end of a funnel member 15 which extends downwardly from this chamber. One end of a drain pipe 16 is coupled to the smaller end of funnel member 15 and the other end of pipe 16 is connected to the inlet end of a receptacle or sump 17. It may be seen that any unatomized oil appearing at the bottom of chamber 3 will be funneled by member 15 into drain pipe 16, and it will then flow via the latter into sump 17. A switch 18 is actuated by a float which is positioned in sump 17 and is responsive to the liquid level therein; when the liquid in sump 17 reaches a certain level, the float-actuated switch 18 is closed, thereby completing a circuit between one lead L2 of a power line and a pump 19. The other power lead L2 is connected directly to pump 19, so that when switch 18 closes, pump 19 is energized.

The pump 19 is preferably a low-pressure, pulse-type or diaphragm-type pump, and may be similar to an electric fuel pump often used on automobile engines. Pump 19 has its intake coupled to sump 17, and its discharge connected to one end of a pipe 20 which extends upwardly and whose opposite end feeds into the oil reservoir or tank 2.

In operation, liquid fuel not atomized in chamber 3 flows downwardly into sump 17, where it collects. When the liquid in sump 17 reaches a predetermined level, the float-switch 18 closes to energize pump 19. The latter then operates to pump the unatomized oil from sump 17 to the fuel reservoir 2, by way of pipe 20. From reservoir 2, of course, this oil can flow downwardly via pipe 1 to the atomization chamber 3, there to be resubjected to the atomization process. Thus, unatomized oil is prevented from accumulating in chamber 3, since it is removed therefrom to sump 17 and then pumped up to reservoir 2. Pump 19 is energized long before the liquid level can reach the upper end of pipe 16.

The invention claimed is: r

1. For use with a liquid fuel burner, an arrangement for atomizing the liquid fuel prior to combustion comprising a chamber, a plurality of ultrasonic compressional wave vibrators arranged in superposed labyrinthine form in said chamber, means for feeding liquid fuel to said chamber in such a manner as to flow in cascade fashion over said vibrators, said vibrators acting to atomize the liquid fuel flowing thereover; and means for removing the atomized fuel from said chamber.

2. An arrangement as defined in claim 1, wherein each of said vibrators comprises an elongated member mounted for vibration in said chamber, the atomizing arrangement including also electromechanical transducer means coupled to all of said members to drive the same at a predetermined ultrasonic frequency.

3. An arrangement as defined in claim 1, wherein the removing means comprises means for producing a flow of air through said chamber in a direction generally transverse to all of said vibrators.

4. An arrangement. as defined in claim 1, including also means for removing from said chamber the fuel remaining unatomized after cascading over said vibrators.

5. An arrangement as defined in claim 1, wherein each of said vibrators comprises an elongated member mounted for vibration in said chamber, the atomizing arrangement including also electromechanical transducer means coupled to all of said members to drive the same at a predetermined ultrasonic frequency; and wherein the removing means comprises means for producing a flow of air through said chamber in a direction generally transverse to all of said elongated members.

References Cited in the file of this patent UNITED STATES PATENTS 862,856 Tygard Aug. 6, 1907 908,962 Cramer Ian. 5, 1909 1,320,852 Goubert Nov. 1919 1,939,302 Heaney Dec. 12, 1933 2,621,032 Schellenburg Dec. 9, 1952 2,779,623 Eisenkraft Ian. 29, 1957 

